1. COMPUTER ORGANIZATIONS CSNB123 NSMS2013 Ver.1Systems and Networking1

2. COMPUTER ORGANIZATIONS CSNB123 Architecture Attributes visible to the programmer  Instruction set  Number of bits used for data representation  I/O mechanisms  Addressing techniques Recap Chapter 1 Ver.1Systems and Networking2

3. COMPUTER ORGANIZATIONS CSNB123 Machine Instruction Characteristics TermDescription Machine instruction / computer instructions Instruction which is executed by processor Processor’s instruction set Collection of different instructions that the processor can execute Each instruction must contain the information required by the processor for execution NSMS2013 Ver.1Systems and Networking3

4. COMPUTER ORGANIZATIONS CSNB123 Machine Instruction Characteristics (Cont.) Elements of Machine Instruction (MI) ElementsDescription Operation code (opcode) specifies the operation to be performed ADD, SUB Source operand reference operands that are inputs for the operation Result operand reference the operation may produce a result Next instruction reference tell processor where to fetch the next instruction after the execution of this instruction is complete NSMS2013 Ver.1Systems and Networking4

5. COMPUTER ORGANIZATIONS CSNB123 Simple Instruction Format Instruction is represented by a sequence of bits During instruction execution, an instruction is read into an instruction register (IR) in the processor. The processor must be able to extract the data from the various instruction fields to perform the required operation Opcodes are presented by abbreviations-mnemonics-that indicate the operation..why do this …hard to remember code in binary form NSMS2013 Ver.1Systems and Networking5

6. COMPUTER ORGANIZATIONS CSNB123 Simple Instruction Format (Cont.) Operands also represented symbolically Example:  Add the value contained in the location Y to the contents of register R  Y=refer to the address of a location in memory  R=refers to a particular register NSMS2013 Ver.1Systems and Networking6

7. COMPUTER ORGANIZATIONS CSNB123 Instruction Types HLL language instruction in BASIC Instruct the computer to add the value stored in Y to the value stored in X and put the result in X. NSMS2013 Ver.1Systems and Networking7

8. COMPUTER ORGANIZATIONS CSNB123 Instruction Types (Cont.) Simple instruction sets Load a register with the contents of memory location 513 Add the contents of memory location 514 to the register Store the contents of the register in memory location 513 NSMS2013 Ver.1Systems and Networking8

9. COMPUTER ORGANIZATIONS CSNB123 Instruction Types (Cont.) CategoryDescription Data processingArithmetic and logic instructions Data storageMovement of data into or out of register and or memory locations Data movementI/O instructions Control-test and branch instructions Test instructions are used to test the value of a data word or the status of the operation Branch instructions are used to branch to a different set of instructions depending on the decision made NSMS2013 Ver.1Systems and Networking9

10. COMPUTER ORGANIZATIONS CSNB123 Number of Address Address refer to location that store the value of the operands In most architecture, most instructions have 1,2 or 3 operand addresses NSMS2013 Ver.1Systems and Networking10

11. COMPUTER ORGANIZATIONS CSNB123 Example NSMS2013 Ver.1Systems and Networking11

12. COMPUTER ORGANIZATIONS CSNB123 3 address instructions Each instruction specifies two source operand locations and a destination operation location Operand 1, Operand 2, Result Not common since they require a relatively long instructions format to hold the three address references T = temporary location-to store intermediary result NSMS2013 Ver.1Systems and Networking12

13. COMPUTER ORGANIZATIONS CSNB123 Example NSMS2013 Ver.1Systems and Networking13 InstructionComment SUB Y, A, BY  A-B MPY T, D, ET  D * E ADD T, T, CT  T + C DIV Y, Y, TY  Y / T

14. COMPUTER ORGANIZATIONS CSNB123 2 address instructions Each instruction specifies both an operand and the result location Operand 1, Operand 2, Result MOVE – is used to move one of the values to a result/temp loc before performing the operation Reduce space for address NSMS2013 Ver.1Systems and Networking14

15. COMPUTER ORGANIZATIONS CSNB123 Example NSMS2013 Ver.1Systems and Networking15 InstructionComment MOVE Y, AY  A SUB Y, BY  Y – B MOVE T, DT  D MPY T, ET  T * E ADD T, CT  T + C DIV Y, TY  Y / T

16. COMPUTER ORGANIZATIONS CSNB123 1 address instructions Second address must be implicit (hidden) Common in earlier machines- the implied address being a processor register known as the accumulator (AC) The AC contains one of the operands and is used to store the result NSMS2013 Ver.1Systems and Networking16

17. COMPUTER ORGANIZATIONS CSNB123 Example NSMS2013 Ver.1Systems and Networking17 InstructionComment LOAD DAC  D MPY EAC  AC * E ADD CAC  AC + C STOR YY  AC LOAD AAC  A SUB BAC  AC – B DIV YAC  AC / Y STOR YY  AC

18. COMPUTER ORGANIZATIONS CSNB123 0 address instructions All address must be implicit (hidden) Stack-based operations  last-in-first-out (LIFO) set of locations  Interact with the stack using PUSH and POP operations PUSH – to push a data from memory onto the stack POP – to pop out data from the stack to a memory location NSMS2013 Ver.1Systems and Networking18

19. COMPUTER ORGANIZATIONS CSNB123 Example NSMS2013 Ver.1Systems and Networking19 Instruction PUSH A PUSH B SUB PUSH C PUSH E PUSH D MPY ADD DIV POP A PUSH B PUSH A A B A SUB A PUSH C C A PUSH D C D A PUSH E C D E A C MPY D A C ADD A DIV POP

20. COMPUTER ORGANIZATIONS CSNB123 Number of Address (Cont.) Fewer address  require less complex processor  Instruction become shorter  But contain more total instructions-longer execution time NSMS2013 Ver.1Systems and Networking20

21. COMPUTER ORGANIZATIONS CSNB123 Number of Address (Cont.) Multiple address instructions – have multiple general purpose register Register references are faster than memory references – speed up the execution Most contemporary machine employ a mixture of 2 and 3 address instructions NSMS2013 Ver.1Systems and Networking21

22. COMPUTER ORGANIZATIONS CSNB123 Types of Operands Categories of data  Addresses  Numbers Integer/floating point  Characters ASCII etc.  Logical data 0/1-false/true NSMS2013 Ver.1Systems and Networking22

23. COMPUTER ORGANIZATIONS CSNB123 Types of Operations Data transfer Arithmetic Logical Conversion I/O Transfer of control NSMS2013 Ver.1Systems and Networking23

24. COMPUTER ORGANIZATIONS CSNB123 Types of Operations (Cont.) NSMS2013 Ver.1Systems and Networking24

25. COMPUTER ORGANIZATIONS CSNB123 Types of Operations (Cont.) NSMS2013 Ver.1Systems and Networking25

26. COMPUTER ORGANIZATIONS CSNB123 Control Operations Branch/jump instruction  Sequential  Unconditional branch  Conditional branch Skip Subroutine / procedure call NSMS2013 Ver.1Systems and Networking26

27. COMPUTER ORGANIZATIONS CSNB123 Control Operations - Branch Has one of its operands the address of the next instruction to be executed A sequence of code in a computer program which is conditionally executed depending on whether the flow of control is altered or not (at the branching point)  Conditional – the branch is made only if a certain condition is met  Unconditional – a branch instruction in which the branch is always taken NSMS2013 Ver.1Systems and Networking27

28. COMPUTER ORGANIZATIONS CSNB123 Control Operations - Branch (Cont.) BranchExplanation Sequential Normal execution One instruction after the other Unconditional branch Non-sequential instruction at the designated address is unconditionally executed Conditional branch Non-sequential A branch is made conditionally to another instruction address. If the condition is true, the instruction at the designated address is executed. NSMS2013 Ver.1Systems and Networking28

29. COMPUTER ORGANIZATIONS CSNB123 Control Operations - Skip Useful in loop control Implies that next instruction to be skipped NSMS2013 Ver.1Systems and Networking29

30. COMPUTER ORGANIZATIONS CSNB123 Control Operations – Subroutine Also known as procedure call A self-contained computer program that is incorporated into a larger program At any point in the program, the procedure may be called or invoked The processor is instructed to go and execute the entire procedure and then return to the point from which the call took place A procedure allow the same piece of code to be used many times Involves two basic instructions; call and return instruction NSMS2013 Ver.1Systems and Networking30

31. COMPUTER ORGANIZATIONS CSNB123 Control Operations – Subroutine (Cont.) Call instruction Instructions that branches from the present location to the procedure Return instruction Instruction that returns from the procedure to the place from which it was called NSMS2013 Ver.1Systems and Networking31

32. COMPUTER ORGANIZATIONS CSNB123 Control Operations – Subroutine (Cont.) NSMS2013 Ver.1Systems and Networking32